JP2954599B2 - Write device drive circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writing apparatus for writing writing data based on image information to a photoconductor, and more particularly to a light and heat writing apparatus.

2. Description of the Related Art An optical writing device for writing image information on a photoconductor by a laser beam is used in a printer or the like.

In most cases of this type of optical writing device, binary writing is performed by turning on / off a beam.

Therefore, in order to express halftones, it is necessary to specify a method called area gradation. This expresses, for example, 16 levels of gradation in units of 4 × 4 dots 1 in length and width. Therefore, according to this area gradation, since four dots are one pixel in the vertical direction, the pixel density becomes 1/4. Similarly, a pixel density of 1/8 is required to provide 64 levels of gradation. If the writing density is increased, for example, by a factor of 8, the pixel density will be compensated, but the laser beam optical system also has a limit, and the practical limit is about 16 dots / mm.

On the other hand, when the output image of the printer is also used as a digital copying machine, at least 64 gradations are required.

Under these circumstances, if one dot is represented by multiple values (for example, four values) instead of ON / OFF (binary), 64 levels of gradation can be obtained in combination with 4 × 4 area gradation. Can be expressed. That is, the multi-value of one dot can relatively increase the pixel density.

In order to modulate the laser beam into multiple values, there are a method of changing the laser power (power modulation) and a method of changing the pulse value.

However, since the former requires a margin for the temperature characteristics of the power output of the laser diode and the light output, it is difficult to provide many levels.

On the other hand, the latter does not have such difficulty and can take many levels depending on the modulation circuit. For example, RWM is performed by creating a saw-tooth plate using an RC charge / discharge circuit and slicing the sawtooth plate with an analog level signal.

However, this method has a problem in high-speed processing because an analog circuit is used. In addition, the stability of the analog level is poor, and it is necessary to perform temperature compensation and correction of variations due to components.

Conventionally, there have been various difficulties as described above regarding multi-valued laser beams.

Therefore, the present applicant has previously proposed Japanese Patent Application Laid-Open No. 62-287773. It has one or more phase circuits for shifting the phase of the clock signal, a logic circuit for comparing the output of the phase circuit and the clock, and a selection circuit for selecting a plurality of outputs of the logic circuit. This is intended to achieve this by modulating the pulse width of the data according to the applied signal and driving the write element.

According to the writing device drive circuit according to the present invention, the setting of the multi-valued level can be performed completely digitally, the level stability and reproducibility can be improved, and the performance variation during mass production is small. .

[Problems to be Solved by the Invention] When one dot of the beam is multi-valued, it is required that each multi-valued level can be reproduced stably and each level can be set independently. Furthermore, in order to achieve better gradation expression, it is necessary that each pulse width can be finely adjusted according to the light attenuation characteristics of each photoconductor. Also,
In a printer (for example, a color printer or the like) in which a plurality of photoconductors are exposed with respective scanning beams to form an image and are superimposed and transferred, the pulse width needs to be further adjusted.

The present invention has been made based on such a background, and an object of the present invention is to perform a writing level and multi-leveling in a stable and simple configuration in an optical writing system or the like using a laser beam, and Another object of the present invention is to provide a writing device drive circuit capable of finely adjusting a pulse width necessary for gradation expression.

Means for Solving the Problems The object is to provide a writing device that reads image information, obtains writing data converted into an electric signal, and performs digital writing on a photoconductor in accordance with the writing data and a data clock signal. One or more phase circuits that output a plurality of signals having different phases by shifting the phase of the data clock signal, and are provided corresponding to the phase circuits, respectively, and one of the outputs of the phase circuit is selected. A phase selection circuit, a plurality of logic circuits that take a logical product or a logical sum of the output of each phase selection and the data clock signal, and a signal having a different pulse width from each of the plurality of logic circuits. And a selection circuit for selecting according to the level of the write data.

[Action]

The means selects one of a plurality of signals having different pulse widths respectively output from the plurality of logic circuits in accordance with the level of the write data, based on the level of the write data.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram showing a first embodiment of a writing device drive circuit according to the present invention, FIG. 2 is a timing chart of each signal of the first embodiment, and FIG. 3 is a writing circuit according to the present invention. FIG. 4 is a block diagram showing a second embodiment of the device drive circuit, and FIG. 4 is an explanatory view schematically showing a laser printer to which the writing device drive circuit according to the present invention is applied.

First, a laser printer to which the writing device drive circuit is applied will be described with reference to FIG.

12 is a laser diode, 13 is a polygon mirror, 14 is a photosensitive drum, 15 is an fθ lens, 16 is a condenser lens, 17 is a cylindrical lens, 18 is a mirror, and 19 is a photodetector for keeping the writing position constant. is there. In such a configuration, the beam emitted from the laser diode 12 is converted into a parallel beam by the condenser lens 16, and the parallel beam is linearly focused on the polygon mirror 13 by the cylindrical lens 17. The beam reflected by the polygon mirror 13 is focused on the photosensitive drum 14 by the fθ lens 15, and the beam scans the photosensitive drum 14 by the rotation of the polygon mirror 13.

Next, a first embodiment will be described with reference to FIG. 1 and FIG.

In the present embodiment, a pulse width modulation method is adopted, and this is subjected to digital processing.

In this example, two bits D0 and D1
The selector 11 selects four levels including (OFF). The D latch 1 synchronizes the data D0 and D1 with CLK.

Now, how to make a pulse width will be described. The block composed of the delay element 2, the phase selection means 3 and the logic circuit 8 is a block composed of the delay element 4, the phase selection means 5 and the logic circuit 9 or the delay element 6, the phase selection means 7 and the logic circuit 10. Since this is functionally equivalent to this, one of the blocks will be described.

Data black poke CLK generates clock a _o ~a _m displaced multiple phase is input to Deirei element 2. These a _o
~a _m are respectively inputted to the phase selecting unit 3, of which 1
Two clocks C1 are selectively output. Obtaining a short pulse signal P ₁ from Deyutei the clock by AND (Rojitsuku circuit 8) with C1 to CLK. In Rojitsuku circuit 10 OR, in this case, it will get a long pulse signal P ₃ from Deyutei the clock.

FIG. 2 is a timing chart. Figure 2 is among the plurality of different phases CLK signal a _o ~a _m made of Deirei element 2 based on CLK, for example C ₁ by the phase selecting unit 3
= Selecting a ₁ becomes a signal, the output of Rojitsuku (AND) circuit 8, an AND output p ₁ between CLK and a _1. Of a _o ~a _m in accordance connexion selecting means 3, it can be adjusted pulse width of Yotsute P ₁ in which one to choose. The same applies to the other pulse signals P ₂ and P ₃ .

One of the pulse signals P _{0 to} P ₃ thus produced is
One is selected by the selection circuit 11 by the data D0 and D1, and _Pn is output. By directly modulating the laser diode 12 with this signal _Pn , the dot diameter to be written is multivalued. As the phase selecting means 3, 5, 7, for example, a mechanical switch for selecting one of multiple inputs may be used, or a selector like the selector 11 may be used.

FIG. 3 shows a second embodiment, in which phase selecting means 3,
Selectors are used for 5,7. In this case, it is possible to change the selection value (a _o ~a which one pick of _m) from the outside, change the image quality (changing eg r curve) or when, or aging conditions, such as process it is also possible to change the selection value S ₀ to S ₂ in response to changes.
In this case, a predetermined selection value may be set corresponding to a certain mode, or a change over time may be detected and fed back.

[Effects of the Invention] As described above, according to the present invention, one of a plurality of signals having different pulse widths respectively output from a plurality of logic circuits in accordance with the level of write data is changed to the level of the write data. , The multilevel level can be set completely digitally, the level stability and reproducibility can be improved, and the performance variation during mass production can be reduced. Further, since the circuit configuration is made up of only basic logic elements, it is simple and low-cost, and high-speed operation can be performed up to the response speed of the logic elements. Also, by making the pulse width of each pulse signal output from the logic circuit variable, it is possible to set the pulse width so as to obtain better gray balance.

[Brief description of the drawings]

All the drawings are for explaining the embodiment of the present invention. FIG. 1 is a block diagram showing a first embodiment of a writing device drive circuit according to the present invention, and FIG. 2 is a block diagram of the first embodiment. FIG. 3 is a block diagram showing a second embodiment of the writing device drive circuit according to the present invention, and FIG. 4 is a timing chart of a laser printer to which the writing device drive circuit according to the present invention is applied. It is explanatory drawing which shows an outline. 2,4,6 …… delay element, 3,5,7 …… phase selection means, 8,9,
10 ... Logic circuit, 11 ... Selector.

Claims (1)

(57) [Claims] 1. A writing device for reading image information and obtaining write data converted into an electric signal, and performing digital writing on a photoconductor in accordance with the write data and a data clock signal, wherein a phase of the data clock signal is shifted. One or more phase circuits that output a plurality of signals having different phases from each other, a phase selection circuit that is provided corresponding to each of the phase circuits, and selects one of outputs of the phase circuit, A plurality of logic circuits for performing an AND operation or an OR operation on the output of the phase selection circuit and the data clock signal; and outputting signals having different pulse widths respectively output from the plurality of logic circuits in accordance with the level of the write data. And a selection circuit for selecting.